Hemispheric Contribution to Exploration of Space Through the Visual and Tactile Modality

Control and unilaterally brain-damaged patients were given two tests requiring the exploration of space through the visual and the tactile modalities and this finding lends support to the hypothesis that hemi-inattention does not depend so much on perceptual and motor factors as on a mutilated representation of space.

Abstract

Control and unilaterally brain-damaged patients were given two tests requiring the exploration of space through the visual and the tactile modalities. In the visual test, the patient was required to identify a number on a display board among alternatives, while in the tactile test he had to find a marble in a maze. The score was the time spent in searching for the item. On the visual test, controls performed better when the item was on the left side than when it was on the right. This “normal” left-right gradient (probably due to reading habits) was found to be significantly increased in left brain-damaged patients and reversed in right brain-damaged patients, a finding which supports the assumption that injury to one hemisphere mainly impairs the exploration of contralateral field. On the tactile test, each hemispheric group performed worse in the contralateral field. This lengthening of the searching time cannot be explained by disruption of the sensorimotor mechanism subserving space exploration and points to the impairment of a higher level ability, identifiable as the representation of contralateral space. When performance was scored in terms of failure in finding the marble within the 90 sec time limit, right hemisphere patients with visual field defects turned out to be significantly more impaired than any other brain-damaged subgroup. This finding is suggestive for the occurrence of unilateral neglect also in the tactile modality and it lends support to the hypothesis that hemi-inattention does not depend so much on perceptual and motor factors as on a mutilated representation of space.